An optical power splitter splits incoming power into two output ports with pre-determined power ratio and is used in optical systems for signal/power distribution, monitoring, combining, and attenuation. These functions can be realized using Fused Biconical Taper (FBT), Planar Lightwave Circuit (PLC), and Micro-Optic (MO) lens/filter technologies and have found good results in single mode applications. In a multimode fiber application, the number of optical modes excited and the power distribution among them can vary wildly which results in coupling ratio and propagation time delay variation, collectively referred to as modal noise. Especially in a high bit-rate multimode fiber system, modal dependent intensity noise and modal dependent timing jitter translate into the closing of eye diagram and can significantly impact system performance.
FIG. 1 illustrates an open eye diagram versus a degraded eye diagram due to the modal dependent intensity noise and modal dependent timing jitter. The modal dependent intensity noise causes the eye diagram to compress vertically while the modal dependent timing jitter causes the eye diagram to close horizontally.
The coupling mechanism used in the realization of power splitters can be categorized into two types: a side coupling mechanism such as FBT and an end coupling mechanism such as MO. FIG. 2 illustrates the mode coupling mechanism in end coupling devices and side coupling devices. The overlap region between two mode profiles is responsible for the power coupling from one fiber to the other fiber. Since the side coupling mechanism depends on the tail region overlap of optical mode profiles, a weak coupling, it is more susceptible to modal noise. The end coupling mainly depends on the center region overlap of the mode profiles, a strong coupling mechanism, which makes it more resistive to modal noise. Power splitters that employ end coupling mechanism are less susceptive to modal dependent intensity noise and modal dependent timing jitter than splitters that use side coupling mechanism.